Funding for this research was provided by:
National Natural Science Foundation of China (21377167, 21677177)
Text and Data Mining valid from 2019-05-27
Received: 8 April 2019
Accepted: 10 May 2019
First Online: 27 May 2019
Ethics approval and consent to participate
: Not applicable.
: All authors agreed to publish the paper.
: The authors declare that they have no competing interests.